The present invention relates to automatic fire sprinklers, and more particularly, to automatic fire sprinklers having a variable, self-adjusting orifice for improving the performance of the sprinkler by changing the amount and flow-rate of the discharged water.
Typically, an automatic fire sprinkler includes a body with a base, an inlet connected to a source of pressurized water, or fire retardant fluid, and an outlet, both defined by the base, a passageway between the inlet and outlet, and a flow-adjusting orifice, usually located upstream close to the outlet. Additionally, a plug closing the outlet when the sprinkler is in standby condition is held in place by a thermally sensitive element. When the temperature is elevated to a pre-determined value, the thermally sensitive element disintegrates. Consequently, the water pressure urges the plug away from the outlet, enabling the sprinkler to discharge. A supported deflector distributes the water stream flowing from the outlet, dispersing the stream over the region to be protected by the sprinkler.
The various requirements of automatic fire sprinklers are defined in the National Fire Protection Association (NFPA) 13 Standard for the Installation of Sprinkler Systems, which was also adopted by American National Standards Institute (ANSI). The NFPA standard includes the minimum required amount of water for extinguishing a fire in a specified area of the fire source. This specified area of the fire source is empirically determined by standard tests according to the hazard occupancy of goods in a warehouse.
Generally, the water flow rate “Q” from a sprinkler is determined by the formula:Q=K*(p)1/2where “K” represents the nominal sprinkler discharge coefficient, known as the K-factor, and “p” represents the pressure at the inlet to the sprinkler. The K-factor of a given sprinkler, which mainly depends on the orifice dimensions, is determined by standard flow testing.
Different applications require different water flows, i.e., sprinklers that have different K-factors, and/or different inlet water pressures. For standard coverage, the most commonly used sprinklers have a K-factor of 5.6, while extended coverage applications use sprinklers having larger K-factors of 8 to 11.2, which have correspondingly larger orifices.
An advanced sprinkler, developed during the last two decades, is the low-pressure fast response (LPFR) sprinkler, also known as the early suppression fast response (ESFR) sprinkler. Characteristically, this sprinkler has K-factors between 14 and 25.2, a short time of response, and high water flow rates. Typical prior art examples of these LPFR or ESFR sprinklers are U.S. Pat. No. 5,829,532 and U.S. Pat. No. 6,502,643, both to Meyer, et al., U.S. Pat. No. 6,059,044 to Fischer, and U.S. Pat. No. 6,336,509 to Polan, et al. As will be developed in greater detail hereinbelow, the use of sprinklers having greater K-factors reduces the required water pressure at the inlet, and therefore obviates the need of installing more robust and capital-intensive systems that also require more electrical power and maintenance.
In addition, a lower water pressure results in larger droplets being produced by the deflector. The larger droplets have a higher momentum that assists them in being deflected further from the sprinkler, thereby extending the coverage area.
Alternatively, for a given water pressure, the use of sprinklers having larger orifices increases the flow of water through each sprinkler, thus reducing the required number of sprinklers for the requisite coverage area.
In prior art sprinkler systems, after a fire starts, the thermally sensitive element of the closest sprinkler disintegrates at the pre-determined temperature, permitting Q1 of water to discharge at inlet pressure p1. If the fire has not been extinguished by this sprinkler, additional heat is evolved and spreads, and a second sprinkler discharges. As a result, Q1 and p1 of the first sprinkler decrease to Q2 and p2, since now the same water source is feeding two sprinklers. As additional sprinklers discharge, the values of Q and p of the first and second sprinklers further decrease. Final Q and p values are reached only when no additional sprinklers discharge.
Since the K-factor in all prior art sprinklers is constant and the value of the inlet pressure p changes according to the number of discharging sprinklers, the amount of water discharged by the first sprinkler, according to the above mentioned formula, is Q1=K*(p1)1/2, Q2=K*(p2)1/2 etc. Consequently, in the first stage of the operational pattern, the amounts Q1 and Q2 are greater than the amount discharged by the first-opened sprinkler when more sprinklers are in operation.
The efficacy of existing automatic fire sprinkler systems notwithstanding, it would be highly advantageous to have an improved automatic fire sprinkler system that discharges the requisite amount of water for extinguishing a fire with a decreased number of sprinklers, such that the capital cost for the sprinklers and auxiliary equipment, such as water tanks and pressure pumps, would be greatly reduced. It would be of further advantage if such a system would reduce the water damage caused by current systems. It would be yet of further advantage if the improved performance of the sprinkler system could be obtained in a simple, efficient, and cost-effective fashion, both in new systems and by retrofitting of existing systems.